An estimated 40-60% of human cancers are associated with sex hormone exposure. Examination of the importance of estrogens as carcinogens or cocarcinogens in the development of cancer requires evaluations of estrogen effects during the various stages of estrogen-induced tumor formation. One experimental model for examining the possible role(s) of estrogens in tumor development is the Syrian hamster. Castrated juvenile male golden Syrian hamsters and ovariectomized female Syrian hamsters will produce kidney tumors after prolonged exposure (9 to 12 months) to the steroidal estrogen estradiol (E2) or to the nonsteroidal estrogen diethylstilbestrol (DES). This unique in vivo model of estrogen carcinogenicity may provide important insights into the molecular processes by which estrogens induce cancer development. Recent research with this animal model in our laboratories has shown that estrogens produce dysplastic foci within three months of estrogen treatment in hamsters and identified differences in the extent of estrogen metabolism in primary kidney cell cultures and in kidney tissue slices. The focus of our research is the elucidation of the role(s) of estrogens in biochemical events leading to tumor formation. Our current working hypothesis is that continuous exposure of target cells to estrogens results in hormonally-induced changes in cellular biochemistry. These changes increase the vulnerability of the cells by exposing critical regions of the DNA, by altering metabolism to increase concentrations of potentially reactive compounds, and/or by modifying levels of proteins important for growth and cell division. Genotoxic and nongenotoxic insults at carcinogenic targets in the hormonally-induced cell then result in phenotypic alterations in gene expression. This collaborative, multidisciplinary proposal addresses the hypothesis by developing in vitro cell systems with varying tumorigenic potential and analyzing the effects of various estrogens (agonists, metabolites, antagonists) on parameters during stages of tumorigenesis. The specific aims of this proposal are (1) to establish in vitro cell systems of kidney cells with differing tumorigenic potential, i.e., to exhibit anchorage-independent growth and to produce progressively growing tumors in athymic nude mice, (2) to analyze and compare biomarkers of hormonally-induced changes and altered phenotypic expression in cells with varying tumorigenic potential, (3) to evaluate the changes in phenotypic expression upon in vitro exposure of the cell systems to estrogen agonists, metabolites, and antagonists, and (4) to initiate parallel studies with human breast cells in order to establish in vitro cell systems of differing tumorigenic potentials and effects of estrogen agonists, metabolites, and antagonists.